Combined Ab Initio and Interatomic Potentials Based Assessment of the Defect Structure of Mn-Doped SrTiO3

The energetics of doping SrTiO3 with Mn is investigated using density functional theory calculations within the GGA + U scheme and lattice statics simulations. Defect formation energies are derived for different Mn charge states and for occupation at both the Sr- and Ti-sites. For the GGA + U calculations, due consideration is given to finite-size effects and the treatment of the chemical potential of atomic oxygen to avoid errors associated with direct DFT calculations of the oxygen dimer. The lattice statics calculations have been completed using a recently developed potential model designed for the investigation of rare-earth and transition metal doping of SrTiO3. Intrinsic defects have also been considered in all possible charge states. The GGA + U calculations predict that for the three different thermodynamic environments examined both Mn2+ and Mn4+ ions occupy the Ti-site via either oxygen vacancy compensation (Mn2+) or no charge compensation (Mn4+). This is contradictory to the lattice statics calculations which predict Mn2+ doping at the Sr-site and Mn4+ at the Ti-site. Experiment suggests that Mn2+ doping at both the Sr- and Ti-sites is possible.